I guess the answer was to never go item-centric for gameplay longevity, but instead to have altered the skill system so it was uncapped, but compensate by applying a weighted system so you can't GM every skill, but a limited selection of skills could gain eternally with diminishing returns, and also have player death's damage skill points earned, but high skill levels are rewarded with titles at varying skill levels and other miniscule perks that don't cause gameplay-killing imbalances, and focus hard on anti-cheat and anti-scripting technology from the get go so people don't AFK farm gold and ruin the economy, and never hesitate to ban paying customers who you know for a fact are cheating by referencing server logs of player activity and putting appropriate measures in place to enable that automated analysis, and implement a highly customisable blacksmithy and tailoring system so everyone can have unique appearances and uniquely decorated weapons and continue to expand on it over time without altering underlying item properties, and encourage player interactions to utilise these mechanics by making NPC's for such services infrequently accessible and have them also charge a significant fee when they are around.
Oh, what am I talking about, all that sort of stuff is way too boring and too much effort for any dev team to do ever.
Edit: Oh yeah, and of course, make only 1 client to maintain and using monthly subs to deliver interesting content and large story arcs to keep things rolling, and don't duplicate the entire landmass into two rulesets, splitting the server population up, and to compensate for PvM players; design a sane PvP system and/or use different rulesets for different cities/regions of the world.
(and hated Brittle items).
